1. Field of the Invention
The present invention relates to an inspecting apparatus which is employed to inspect general performance of a photovoltaic devices, such as a photovoltaic cell, a photovoltaic devices string which is formed by connecting the photovoltaic cells in series, a photovoltaic devices panel which is formed by disposing a plurality of photovoltaic strings in parallel, and the like.
2. Description of the Background Art
It is well known that a silicon photovoltaic devices is employed to harness solar energy. In the manufacture of the photovoltaic devices, it is important to evaluate whether the photovoltaic devices has predetermined power generation capacity. The evaluation is usually performed by measuring output characteristics thereof.
The output characteristics are the photovoltaic conversion characteristics obtained by measuring current-voltage characteristics of the photovoltaic devices under light irradiation. As a light source, it is desired to use the solar light. However, since the intensity of the solar light varies in relation to weather, a solar simulator is employed. In the solar simulator, a xenon lamp, a metal halide lamp or the like is employed as an alternative to the solar light. If the aforementioned light source has been lighted for a long time, the temperature thereof rises or the like, leading to a variation on the light intensity thereof. Therefore, by using the flash light of the aforementioned light source, it is able to plot the output characteristic curve of the photovoltaic devices on the basis of collected data by setting a voltage as the lateral axis and a current as the vertical axis (for example, refer to Japanese Patent Application Laid-Open No. 2007-88419).
The following method different from the solar simulator is disclosed in the Patent Document WO/2006/059615. By applying a voltage to a polycrystalline silicon photovoltaic devices element in a forward direction, the photovoltaic devices element emits an electro-luminescence (hereinafter, referred to as “EL”) light. The same occurs in a thin-film typed photovoltaic devices. By studying the EL light emitted from the photovoltaic devices element, it is able to obtain the distribution of current density of the photovoltaic devices element. The defect of the photovoltaic devices element can be determined on the basis of the uneven distribution of current density. Namely, a portion which emits no EL light is determined to be a defective portion, and the photovoltaic devices element is determined to have the predetermined power generation capacity if the total area of the defective portions is smaller than a predetermined amount.
The structure of an inspecting apparatus described in the Patent Document WO/2006/059615 is schematically illustrated in FIG. 7. The inspecting apparatus 10 includes a darkroom 11, a CCD camera 12 which is disposed at an upper portion of the darkroom 11, a power source 14 which applies a current to a photovoltaic cell 13 disposed on the floor of the darkroom 11, and an image processing apparatus 15 which processes image signals from the CCD camera 12.
The darkroom 11 is provided with a window 11a where a finder 12a of the CCD camera 12 is disposed. Therefore, an image to be photographed by the CCD camera 12 can be confirmed by watching with an eye from the finder 12a. As the image processing apparatus 15, a computer is employed.
In the inspecting apparatus 10 illustrated in FIG. 9, the photovoltaic cell 13 is disposed at a lower position and is photographed by the camera from an upper position. However, since the EL light emitted from the photovoltaic cell 13 is a weak light ray of wavelength between 1,000 nm and 1,300 nm, it is not able to be detected unless the photovoltaic cell is disposed inside the darkroom 11. In case that the inspecting object is a piece of photovoltaic cell, the dimension thereof is about 100 nm×100 nm, and the darkroom 11 in which the photovoltaic cell is disposed is small sized.
However, in case that the inspecting object is a photovoltaic devices panel, the dimension thereof is about 2 m×1 m; therefore, the darkroom 11 has to have a dimension capable of housing the photovoltaic devices panel. Further, the photovoltaic devices panel as the inspecting object has to be disposed inside the darkroom so as to be photographed by the CCD camera 12; therefore, a door has to be disposed in the darkroom for transporting the photovoltaic devices panel into or carrying out from the darkroom. If the inspecting apparatus is configured so as to transport the inspecting object into the darkroom, shading effect has to be secured when the disposed door is closed. It is also necessary that the inspecting apparatus is provided with a positioning member and a guide member for transporting the photovoltaic devices in the darkroom. Furthermore, it is also necessary to dispose an electrifying means in the darkroom for applying a current to the photovoltaic devices. Thereby, the inspecting apparatus becomes complicated in structure and expensive in price.
To photograph a large photovoltaic devices panel with one camera, the distance from the camera to the photovoltaic devices panel has to be kept greater, which makes the darkroom become large sized. By moving the camera to photograph the photovoltaic devices panel part by part for several times, the distance from the camera to the photovoltaic devices panel can be kept smaller, making the darkroom become small sized; however, the inspection time become longer. In order to shorten the inspection time by reducing the photographing times, the area of the photovoltaic devices panel to be photographed in one image will become greater; consequently, the resolution of the photographed image will become lower, and therefore it is impossible to inspect the defect accurately.